1. Field of the Invention
The apparatus of the present invention relates generally to material transfer devices. The material transferred might include, but not be limited to, semiconductor wafers, such as Silicon and Gallium Arsenide, semiconductor packaging substrates, such as High Density Interconnects, semiconductor manufacturing process imaging plates, such as masks or reticles, and large area display panels, such as Active matrix LCD substrates.
2. Description of the Prior Art
The transfer of delicate silicon wafers or the like between a plurality of work stations or locations in the manufacture of semiconductor devices presents unique handling problems. The silicon wafers are very delicate and have highly polished surfaces. When the wafers are abruptly moved, they tend to slide. This sliding action can cause the silicon wafers to abrade or alternatively can cause damage to their edges if they collide.
There are numerous devices described in the prior art for transferring silicon wafers. For example:
U.S. Pat. No. 3,823,836 discloses an apparatus which includes a supply carrier with a plurality of ledges to hold the silicon wafers and a withdrawal device having a vacuum chuck. The vacuum chuck is attached to an elevator which raises and lowers the chuck. A horizontal transfer arm coupled to the vacuum chuck is used to transfer the silicon wafer from the supply carrier to a desired work station.
U.S. Pat. No. 3,730,595 discloses a wafer transfer handling apparatus having an indexable carrier for transferring wafers to and from work stations. Wafers enter and leave the wafer carrier on an air slide with the aid of a wafer ejector acceptor arm having directional air jets. The wafer ejector acceptor arm controls the driving of the wafers into or out of the carrier from or onto the air slide, which moves the waters to or from a work station.
U.S. Pat. Nos. 4,062,463, 3,874,525 and 4,208,159 also disclose wafer transfer devices which include either pneumatic components or gripping devices for handling the wafers.
U.S. Pat. Nos. 4,666,366 and 4,909,701 disclose wafer transfer handling apparatus having an articulated arm assembly which extends and retracts in a "froglike" motion to transfer an object such as a wafer between a plurality of locations. Two articulated arms are operatively coupled such that when one arm is driven by a motor the articulated arms extend and retract in a "froglike" or "frogkick" type of motion. A platform is coupled to the arms and has the object to be transferred disposed thereon.
U.S. Pat. No. 4,951,601 discloses wafer transfer handling apparatus having an articulated arm assembly which includes a concentric-shaft, rotational drive system. However, such drive system requires rotary seals which can contaminate the vacuum chamber. In the drive system of U.S. Pat. No. 4,951,601 the inner shaft 98 is mounted on a drum 111 which is rotated by a cable 113 mounted on a drive 115 which is rotated by a belt. It appears that the drive 115 rotates in an aperture in the vacuum chamber, thus requiring a rotary seal. The hollow middle shaft 96 is mounted on a drum 101 which is rotated by a cable 103 mounted on a drive 100 which is rotated by a belt. It is not clear which components are inside the vacuum, but it seems clear that some rotating member must rotate in an aperture in the vacuum chamber, thus requiring a rotary seal. The device of the present invention has no such rotary seals. All bearings of the present invention are entirely within the vacuum, and all rotating parts are entirely within the vacuum.